EP1095666A1 - Extracorporeal blood purification apparatus - Google Patents

Abstract

Blood purification system includes means (10-13) for measurement of pressure drop across filter (4) or flow rate to the filter evacuation pipe (5). A threshold value for either of these values is determined and is used to compare with a measured value. An exchange controller uses the comparison value to calculate flow rates through pipes (7', 7) connecting substitution source (S) with filter and blood extraction tube (1).

Description

The present invention relates to a device for purifying blood comprising an extraction conduit for blood, a blood return duct, filtration means blood between the extraction duct and the duct back, means to circulate blood, a liquid discharge conduit from said means filtration called ultrafiltrate, means to make circulate the ultrafiltrate in said exhaust duct, a alternative solution source, two connecting conduits between this source and on the one hand, said extraction duct blood, on the other hand, said blood return duct and means to circulate the substitution solution in each of said connecting conduits.

The purpose of extracorporeal purification is on the one hand to clean the blood of patients by removing items undesirable and secondly to control the weight of patients. The invention applies more particularly to hemofiltration which is distinguished from dialysis by the fact that the purification takes place by convection rather than by diffusion through a semi-permeable membrane. In both if the operator is called upon to intervene during the sessions, in particular to avoid coagulation in the circuit extracorporeal circulation, which occurs in particular at filter level.

The coagulation of the extracorporeal circulation in hemofiltration is conventionally reduced by employing anti-coagulants (heparin, liquemine) and proceeding at intervals regular flushing of the circuit and change filters.

Often well tolerated by patients in doses usual, the use of anticoagulants is contraindicated in some cases, for example for patients with significant lesions.

As for rinsing, it is an operation which consists in momentarily circulate physiological fluid in the filter in place of blood. This is done by obstructing the blood extraction conduit with a clamp, connecting a pocket of physiological liquid at the extraction duct blood, waiting for a sufficient amount of fluid physiological has elapsed, usually 100 to 300 ml. This quantity is considered suitable for cleaning the filtered. The flow conditions are then restored to continue treatment. This suite takes a long time and can lead to handling errors. In addition, it interrupts the treatment and the operator must take into account the excess liquid injected into the patient in calculating the water balance of this latest.

In case a filter change is necessary, it return blood to patient, rinse new filter then continue treatment. This operation is long and expensive, so avoid it as much as possible.

Note also that the coagulation phenomenon is added often that of fouling which is a deposit of molecules on the surfaces of the extracorporeal circulation and in particular the walls of the filter. This fouling also reduces the purifying capacities of the blood and is eliminated in the same way way that coagulated deposits. In the rest of the text we uses one of the terms coagulation or fouling interchangeably to designate the two phenomena.

We have proposed in WO 83/04373 an apparatus for producing automatic rinsing by actuating clamps electromechanical at time intervals prescribed by the operator. Patent EP 0 235 591 proposes to add a clamp that allows you to vary the pressure in the filter to increase the effect of rinsing. The downside of these two solutions lie in the fact that these rinses are decided by the user who has only a rough idea the coagulation speed of the system. Therefore, either the rinsing is too frequent, which decreases the efficiency of treatment by repeated interruptions of this last, or it is not frequent enough, leading to a coagulation due to insufficient rinsing.

In other known devices, all of the liquid replacement is brought in predilution, increasing thus the flow and dilution of blood in the filter. This has reduces the coagulation of the system, but increases considerably the quantity of substitute liquid consumed and processing time. We know indeed, at high flow rates, at least 30% of the volume injected in predilution passes through the filter without participating in the purification some blood. So, with a treatment requiring for example an exchange volume of 45 liters, the substitution being entirely prediluted, 15 liters of a physiological solution expensive needlessly pass through the filter.

Note that the volume of exchange, to which corresponds a exchange rate, is defined as the volume of liquid participating in the purification of the blood withdrawn from the latter at during the session. If there are no losses, especially by predilution, this volume corresponds to that of ultrafiltrate. It is the data which, in hemofiltration, determines the degree purifying blood during the session, which could also be defined as the amount of impurities removed from the blood.

None of the systems mentioned above is actually satisfactory since they do not adapt to variations in operating parameters that may appear during the treatment. In addition, patients are regularly insufficiently purified because the prescribed volumes are calculated assuming that all of the liquid substitution is injected in post-dilution, the values not being corrected to take into account the proportion of this liquid introduced in predilution.

Physical parameters that can influence on the coagulation of the system are numerous. We can include the material and the surface of the filter, the composition and blood flow, dose of anticoagulant prescribed and the desired exchange rate. These parameters may vary during treatment in proportions important and short deadlines. It is therefore impossible for the user, to control the state of the system so to systematically avoid its clotting. This is all more true that the duration of the treatments can be several days and the exchange rates are high, for example twelve liters per hour.

The object of the present invention is to remedy, less in part, to the aforementioned drawbacks.

To this end, the subject of this invention is a device extracorporeal purification of blood of the aforementioned type, according to claim 1.

An essential advantage of this invention lies in the fact that this device does not require intervention of the user during processing.

The device according to the invention makes it possible to minimize the substitute solution consumed and adapt the volume exchange so as to respect, as far as possible, all instructions given by the user.

La figure 1 représente un schéma de cette forme d'exécution;

la figure 2 est un schéma bloc des moyens de calcul 9;

la figure 3 illustre la suite d'opérations pour la mise en marche du dispositif;

la figure 4 illustre la suite d'opérations pour le réglage des débits d'ultrafiltrat et de liquide de substitution, intégrant le calcul du nouveau volume d'échange rendu nécessaire par l'utilisation de la prédilution;

la figure 5 illustre la suite d'opérations pour le réglage du taux de prédilution.

The invention will be better understood with the aid of the description which follows and of the appended drawings, which illustrate schematically and by way of example an embodiment of the device which is the subject of this invention.

Figure 1 shows a diagram of this embodiment;

FIG. 2 is a block diagram of the calculation means 9;

FIG. 3 illustrates the sequence of operations for starting up the device;

FIG. 4 illustrates the sequence of operations for adjusting the ultrafiltrate and substitution liquid flow rates, integrating the calculation of the new exchange volume made necessary by the use of predilution;

FIG. 5 illustrates the sequence of operations for adjusting the predilution rate.

The invention has means of extracorporeal circulation blood composed of an extraction duct 1, a pump 2 to extract blood from patient P's body and a return line 3 to bring the purified blood back into the body of patient P. A filter 4 makes it possible to purify the blood, through a polluted solution discharge pipe 5, called the ultrafiltrate, having a means for controlling flow 6.

A substitution solution conduit 7 connects a substitution solution tank S to the circulation circuit extracorporeal 1, 3. This duct splits in two 7 'and 7 "conduits, the first 7' connecting the liquid source of substitution S to the blood extraction duct 1 in upstream of filter 4, the second 7 "connecting this source S to return line 3, downstream of the filter 4. The flow of predilution liquid through the 7 'conduit is controlled by a peristaltic pump 8. The liquid flow from post-dilution through the 7 "duct is controlled by a 8 'peristaltic pump. The predilution liquid can indifferently be injected upstream or downstream of the pump 2 blood extraction.

Calculation means 9 are used to determine the proportion of the predilution liquid flow and that of post-dilution liquid. Sensors 10, 11, 12, and 13, of pressure or flow are arranged in different places of the blood circulation circuit 1, 3 and the evacuation duct 5 of the ultrafiltrate. These sensors 10-13 are connected to the computing unit 9 to supply it with the necessary parameters in determining the respective quantities of substitute liquid flow rates to be sent through the conduits 7 'and 7 "and corresponding to the predilution values and post-dilution calculations.

The usual components of purification devices extracorporeal which do not intervene directly in the scope of the present invention are not shown. This are in particular the air bubble detectors, the clamp closing the blood return line 3, the leaking blood, blood or fluid warmer substitution and the means of measuring the masses passed.

The flow control means are typically peristaltic pumps or clamps controlled by the unit calculation 9.

The invention also applies to circulation systems single needle extracorporeal and dialysis whether or not including the manufacturing of solutions, as well than combined methods like hemodiafiltration.

The evolution of the coagulation of the filter can be followed by measuring the difference in blood pressure between the inlet and the outlet of the filter 4, the filter pressure, calculated by making the difference in the values supplied by the sensors 11 and 13, and / or the transmembrane pressure P _tM usually defined as the pressure difference between the pressure P ₁₂ of the conduit ultrafiltrate measured by the sensor 12 and the average pressure P _av calculated from the values of the sensors 11 and 13, be P _tm = ((P ₁₁ + P ₁₃ ) / 2) - P ₁₂ .

To achieve treatment goals by avoiding coagulation of filter 4, a system according to the invention adapts the substitute liquid flows in the ducts 7 ′, 7 "so as to maintain the value of the influenced parameters by this phenomenon in their normal operating values and adapts the volume of exchange, and consequently the ultrafiltrate flow, taking into account the liquid flow substitution that has actually passed in the 7 'predilution line, so as to correct its value by deducting the share of substitute liquid that does not have participated in the purification. In addition, the system minimizes the volume of substitute liquid flowing into the 7 'predilution line, to avoid wasting this substitute liquid and reach a better degree of purification in the given time.

The block diagram of the computing unit 9 illustrated by the Figure 2 has an interface 15 using which the operator can enter the specifications for the treatment. This interface 15 is connected to a exchange control 16 which includes a calculation program to control the ultrafiltrate pump 6 and the post-dilution 13 according to indications from among others of interface 15, as well as data and / or rules computation which can be contained in a memory (not shown).

The interface 15 can moreover be connected to a control 17 of an anticoagulant distribution station 18, as well as a control unit 19 of the extraction pump blood 2 which acts according to the operator's indications or predefined flow optimization rules.

The computer 9 also includes a control unit predilution 20 connected on the one hand to the control unit of the exchange value 16 and to a unit of interpretation 21 measurements made by sensors 10-13 and others goes to the predilution pump 8. The control unit of the predilution 20 establishes the initial value of the predilution rate according to the instructions received from the order exchange value 16 or rules or values previously recorded in unit 20. The latter increases or decreases the flow rate of the predilution pump 8 in function of the interpretation of the values measured by the detectors 10-13, provided by the interpretation unit 21. Alternatively, the exchange value control unit 16 provides directly to the predilution control unit a set value to be applied to the predilution 8, said value being established on the basis of calculation rules recorded in the calculation means 9. An example of such a rule is to maintain the pre-dilution set point to zero for ultrafiltrate flow lower than a given value, then increase said flow predilution according to a curve proportional to the increase of the ultrafiltrate above said given value.

As described in the following operations relating to the start-up illustrated in Figure 3 of the device extracorporeal circulation, the operator adapts, beforehand the actual processing, the volume of exchange and the duration of treatment, the initial ultrafiltrate flow being calculated by dividing volume by duration prescribed. The substitute liquid flow is adapted to that of ultrafiltrate corrected for values (weight losses required, external contributions and losses) necessary to maintain or adjust the patient's weight as requested by the operator and split in half according to an initial ratio between post-dilution and predilution, determined on bases statistics.

As shown in Figure 4, during processing, the amount of substitute liquid flowing into the 7 'predilution line is measured or calculated, its value being used to determine a new trading volume corresponding to a degree of purification identical to that determined by the volume initially prescribed. The flow 5 ultrafiltrate is then adapted to match to this new volume of exchange, and if possible to reach the purification and weight variation objectives of the patient within the prescribed treatment time.

The physical limits of the material are recorded in calculation unit 9, such as for example the limits of means of controlling the flow rates and the limit of the linear ratio between the decrease in the degree of purification and the value of predilution which appears by increasing the flow of liquid in the predilution duct 7 '. The point beyond which the degree of purification is considered to be insufficient compared substitution fluid consumed is determined by blood and filter variables involved in the coagulation. It can be determined experimentally and recorded in computing unit 9 or measured so continuous, for example by dosing of urea and its variation in the ultrafiltrate 5. To determine if a limit theoretically exceeded, the admissible limit value of the corresponding parameter is memorized. If a value admissible limit is exceeded, the calculation unit assigns the value of the parameter at its limit value and extends the processing time beyond the time required to allow achieve the desired goals.

Since the more blood flow extracted from the patient the higher the better the filtration conditions of the device, it may be advantageous to add a flow sensor 14 on the extraction duct 1 to optimize this flow. To this end, the control unit 19 of the blood extraction pump 2, periodically increases the speed of this pump 2 until the increase in flow of extracted blood no longer increases linearly with increasing the speed of pump 2, thus indicating that the maximum permissible throughput of the access has been exceeded patient's vascular system. At this time, the control unit 19 of the blood pump 2 decreases the speed of this pump 2 in order to reach the last known value to be in the linear range.

This check can be performed repeatedly during treatment so as to maintain blood flow in optimum filtration conditions. The flow sensor 14 will advantageously also be used to determine so specifies the blood flow.

The anticoagulant flow can be zero or not, brought by an auxiliary syringe pump or by a pump 18 controlled by the computing unit 9.

To determine flow rates in accordance with the invention, the computing unit 9 can have the architecture shown in Figure 2, the invention not being limited to this example.

Device configuration data is saved initially, usually outside of a session therapeutic, in calculation unit 9. These data can include the definition of standard treatments, in particular the name of the treatment, the volume of exchange, the duration required and the pipes and filters used, and those of the intakes and loss of liquids external to the device, in particular the type of contribution or losses, the default flow and the mass at achieve. These values can be changed during treatment, the device then taking into account the news values.

At the start of the session, the operator indicates the values of prescribed treatment, for example the water balance of the patient, desired weight loss or infusion. Yes necessary, it modifies the initially defined values which appear by default. This start-up of the device is illustrated by the diagram in Figure 3. The blood flow is defined by one of the methods described previously. The calculation unit 9 then determines the flow initial ultrafiltrate and substitution fluid, the predilution rate being either zero or calculated on the basis rules previously defined and saved in the device. Ideally, the initial predilution rate will be close to the normal operating value at which expect. Treatment begins and pressures transfer and / or transmembrane are measured so as to determine in a few seconds their normal values of functioning which correspond to a stable state of device satisfying its operation according to the rules predetermined.

During treatment, the flow rates of the different pumps 2, 6, 8 and 8 'are adjusted automatically, either at intervals of regular time, either on the basis of an event determined like for example a sharp increase in pressure, by measuring the pressure values 10-13 and by comparing these values to those considered to be the normal operating values. We can thus determine a variable with three states which notably defines if it is necessary reduce, increase or maintain the predilution rate.

The predilution rate is then adjusted according to of the value of the three-state variable and then the volume necessary exchange is calculated, the ultrafiltrate flow being adapted to this new value.

The rules for determining said variable to three states can be defined in several ways, by example, we decrease the predilution rate in each cycle adjustment as long as pressures do not increase no more than 10% from the value determined as being that of operation, or as long as the pressures do not not show an increase of more than 5% by 30 seconds. In the same way we can determine criteria maintaining and increasing the predilution rate. The setpoints of pumps 6 and 8 'are then adapted taking into account the new setpoint of predilution.

A variant consists in providing the pressure measurements 10-13 to unit 16 which then calculates the setpoints for pumps 6, 8 and 8 'taking into account the measures and rules of calculation previously saved.

It is also possible to use other variables that pressures. Ultrafiltrate flow measurements for given pump speeds or clamp openings are also indicators of the level of fouling of the filtered.

Because the parameters that influence the levels normal pressure changes during treatment it will useful to modify them during processing. A way possible is to consider any stable level during at minus 5 minutes as the new normal operating level.

The adaptation of the predilution share may not sufficient to sufficiently clean the filter 4. So if this last clogged, which is for example determined by a transmembrane pressure value greater than a limit defined beforehand or by a rapid increase in said pressure, cleaning is carried out by stopping the blood extraction pump 2, ultrafiltrate pump 6 and that of postdilution 8 'for a duration or for a volume or a given mass of return liquid and actuating that of predilution 8 so as to circulate physiological solution instead of blood and rinse thus the filter 4. The mass of solution injected into the patient during the rinsing thus carried out is then deducted during further processing.

The benefit of the invention is threefold: Reduction of the amount of sterile alternative medical solution expensive used, removing traffic clogging extracorporeal without compulsory addition of anticoagulants and automatic adjustment of the exchange volume for obtain the desired degree of purification.

Claims (10)

Extracorporeal blood purification device comprising a blood extraction conduit (1), a blood return (3), blood filtration means (4) located between the extraction duct (1) and the return (3), means (2) for circulating the blood, a discharge conduit for the ultrafiltrate (5) issuing from said filtration means (4), means (6) for circulating the ultrafiltrate in said discharge conduit (5), a source of substitution solution (S), two connection (7 ', 7 ") between this source (S) and on the one hand, said blood extraction conduit (1), on the other hand, said conduit blood return (3) and means (8, 8 ') to make circulate the substitution solution in each of the said connecting conduits (7 ', 7 "), characterized in that it comprises further means (10-13) for measuring at least one parameters influenced by the resistance of the means of filtration (4) at the flow of the liquid, means (22) to determine at least one threshold value of said parameter, means (21) for comparing said parameter with said threshold value, exchange control means (16) to calculate the distribution of the respective flows at through said connecting conduits (7 ', 7 "), capable of reducing the difference between the value of said measured parameter and said threshold value. Device according to claim 1, characterized in that said measuring means (10-13) of at least one of parameters influenced by the resistance of the filtration means (4) at the flow of the liquid, measure at least one value capable of determining the transmembrane pressure or the pressure transfers from said filtration means (4). Device according to claim 1, characterized in that said measuring means (10-13) of at least one of parameters influenced by the resistance of the filtration means (4) when the liquid flows, measure the flow ultrafiltrate through the exhaust duct (5). Device according to one of the preceding claims, characterized in that said means (22) for determining at least one threshold value of said parameter, calculate this threshold value based on several of said parameters measured or the evolution over time of minus one of said parameters. Device according to one of the preceding claims, characterized in that it comprises means (21) for detecting that at least one threshold value has been exceeded, said values exchange control means (16) being programmed for stop said means (2, 6, 8 ') for circulating the blood, ultrafiltrate and fluid replacement in said connecting conduit (7 ") connecting said source of replacement liquid (S) at said return duct (3), while said means (8) for circulating liquid substitution between said source of substitution liquid (S) and said extraction duct (1) are actuated, until a volume, a mass of substitute liquid or a specified period has elapsed. Device according to one of claims 1-4, characterized in that it comprises means (21) for detecting exceeding at least one threshold value, said predilution control means (20) being programmed to modify the setpoint of the flow rate of the means of circulation of the fluid (8) between said source of liquid substitution (S) and said blood extraction conduit (1), following this overshoot. Device according to one of the preceding claims, characterized in that said exchange control means (16) are programmed to perform compensation of the exchange volume, established according to the volume or the mass of substitution liquid injected into the duct (7 ') connecting the source of substitution liquid (S) to blood extraction duct (1). Device according to one of the preceding claims, characterized in that the physical flow limits means of circulation of the substitute liquid and the ultrafiltrate (6, 8, 8 ') are recorded in said exchange control (16) and predilution (20) means which are programmed to extend the duration of treatment if the prescribed treatment values cannot be reached over the required duration, taking into account said physical limits recorded debits. Device according to one of the preceding claims, characterized in that the exchange control means (16) are programmed to calculate the flow setpoints for the predilution control means (20), on the basis saved rules. Device according to one of the preceding claims characterized in that said blood extraction conduit (1) includes a flow sensor (14) connected to the calculation (9) which comprises means (19) for determining the maximum flow tolerated by the patient-vascular access system, by increasing the speed of the pump (2) for extracting the blood and comparing the linearity of the increased flow with the increase in the speed of said pump (2), and decreasing the speed of said pump (2) as soon as the ratio flow / speed is no longer linear, to reduce speed from pump (2) to the last value in the range linear.

Images